Fuser for electrostatic image

ABSTRACT

A high temperature chamber encased in an air flow to prevent heat transfer to surrounding areas. Heated by intense input to working temperature, then by alternate input just over and under the maintenance level. High level input during sheet processing regardless of cycle at time of sheet processing.

United States Patent 1191 Gray' et al. Nov. 13, 1973 FUSER FOR ELECTROSTATIC IMAGE [76] Inventors: Donald R. Gray, Chesterland; [56] References Cited Richard W. Germuska, Cleveland, UNITED STATES NTS both of Ohio 3,398,259 8/1968 Tregay et a] 219/216 Filed Mar 3 1971 3,159,735 12/1964 Eisner et al 219/388 X [21] Appl. No.: 120,665 Primary Examiner-C. L. Albritton Related Us. Application Data Attorney-Russell L. Root et al. [63] gtpntijnulaton of Ser. No. 807,052, March 13, 1969, 57 ABSTRACT an o e A high temperature chamber encased in an air flow to [52] U 5 CI 219/216 219/388 250/65 ZE prevent heat transfer to surrounding areas. Heated by I 26'3/6 E 355/9 intense input to working temperature, then by alter- [51] Int Cl G03g 13/20 nate input just over and under the maintenance level. [58] Field (E se 61611 19/216 388- High level input during sheet Pmcessing regardless 263/6 E; 355/9; 118/620, 637; 250/65 T, 65 cycle at Pmessmg- ZE 4 Claims, 3 Drawing Figures PATENTED IIBV 1 3 i975 SHEET 2 BF 2 A Y A M MW ATTORNL FUSER FOR ELECTROSTATIC IMAGE RELATED CASES This is a continuation application of Ser. No. 807,052 filed Mar. 13, I969, and now abandoned.

SUMMARY OF THE INVENTION An object sought and the advantage obtained by this invention is an assured full fusing of electrostatic toner in a compact fuser unit.

A further advantage is obtained in the object of the invention'wherein the high temperature area of the fuser is effectively insulated from the area of an associated electrostatic imaging machine by an air stream.

A further object of the invention is conservation of electrical power.

BRIEF DESCRIPTION OF THE DRAWING DESCRIPTION'OF THE PREFERRED EMBODIMENT The preferred embodiment of the invention is useful with substantially any machine which processes individual sheets of material, such as paper, which are to be subjected to intense heat on one surface for a short period of time. Essentially, this indicates that the invention finds particular utility in the electrostatic imaging art, now popularly employed as copy and lithographic master making machines.

The fuser is composed of an inner substantially closed chamber with an encompassing air jacket housing. The inner chamber is formed by means of an insulated wall 11 on one side and an insulated wall 12 on the other. These walls are configuredto enclose a space which can be heated to toner fusion temperature, and are spaced from each other at the ends in order to create an entranceopening 14 and an exit opening 15.

A sheet guide 17 extends from the entrance to the exit ends. Sheet guide 17 is formed in an open wire grid configuration which will allow air circulation, around a sheet passing through the chamber, and is also, by reason of its open construction, transparent to infrared radiation.

One half of the guide is composed of curved wires 19 held together with cross braces 20. This construction is best seen in the FIG. 1. The second portion of the guide is composed of curved wires2l held by crossbraces 22. When these two guide portions are mounted to the surrounding structure, as illustrated in FIG. 2, they form a closely spaced grid which acts as a guide channel to direct a sheet from the entrance end through to the exit end and prevent sheets from becoming entangled in the housing.

A set of feed rollers 23 drive a sheet into the guide 17, and a set 24 draws a sheet from the guide.

The chamber is heated by a first infrared lamp 25 which is mounted on the end walls of the chamber by end mounting bracket 28, and a second infrared lamp .26 which is mounted by bracket 27.

Heating the chamber by infrared radiation serves a dual function. The resin nature of electrostatic toner material is fusible by any means such as' by oven heating which will elevate its temperature sufficiently, or by infrared radiation. Both of these methods are known and used. There has been some prior effort to use the combination of heat and radiation, with only a moderate degree of success.

oven fusing is obtained by placing heating coils in a chamber and heating the chamber for a considerable period of time to fusion temperature before the first sheet is processed. Such chambers are primarily convection ovens. Processing heat fusible toner in such an oven requires a relatively slow speed through the oven in order to allow the carrier sheet to come to temperature before the toner carried thereon is able to fuse. Such a convection oven is satisfactory if a large enough space is available and adequate ventilation is provided to carry away the oven heat as it escapes.

Efforts to use only infrared radiation have resulted in sheets which are generally fused less than necessary, or if sufficient power is provided by the infrared source, a danger of fire or scorching in some areas is a problem. This is caused by reason of the temperature at or near the lamp being very high in order to provide sufficient fusion power. In the event the sheet is stopped in the vicinity of the lamp, fire is an inevitable result.

According to this invention, an electrical infrared means is placed adjacent to one side of the sheet guide 17 and establishes a radiation field crossing the sheet guide for substantially the entire distance from the entrance to the exit. More specifically, a series of infrared radiation lamps are chosen in order to spread an essentially uniform radiation field from the entrance to the exit ends of the chamber. In the illustrated embodiment, two lamps 25 and 26 are found to be sufficient, and will provide the necessary power in a minimum of space, when controlled according to the teachings of this invention. Excessively hot spot concentration is eliminated and fire danger reduced.

Control is established through the instrumentality of a thermostat tube 32 located within the chamber and between the two infrared lamps, but shielded from direct radiation by the reflectors 29 and 30.

The improved fuser of this invention operates by first supplying 1,600 watts of power through the two lamps 25 and 26 until the chamber of the fuser is brought to an operating condition. High input is employed to reduce the waiting period of time before the machine may be put into operation from a cold start. Thereafter, the chamber is maintained at a substantially lower working fusing temperature by alternating between a power input below that which is necessary to maintain the chamber at fusion temperature, and the power input above that which is necessary to maintain a fusion temperature. This is done rather than to attempt to find a theoretically precise heat loss and compensate for that loss. A resultant time-temperature curve would be a chart of a wavering path crossing the ideal straight line temperature curve.

Heating of the chamber between the walls 11 and 12 will, of necessity, create heat around the chamber.

Whenever this chamber is used within the greater houschamber wall 36 which cooperate to shroud the insulated chamber. The plenum and collecting chamber walls are spaced with openings 40 and 41 coinciding with the entrance and exit openings 14 and 15 of the chamber. The structure of the plenum and the collecting chamber place the entrance and exit openings a distance from the chamber entrance and exit openings and therefore define a'spaced channel between the two structures.

A blower 43 is provided to blow air into the plenum 35, and a similar blower 44 to draw air from the collection chamber 36. Such cooperation causes air to envelop the entire chamber and rush across the chamber entrance and exit openings 14 and 15. Therefore any heat which escapes through the walls 11 and 12 or out of the ends of the chamber is collected in the air envelope and carried away from the chamber. Exhaust piping from the blower 44 may then be provided to conduct the warmed air to any remote exhaust position.

Refer now to FIG. 3 for description of the control of the two lamps through three operating conditions, which provides a superior fusion action with sufficiently lowered power requirements.

The thermostat tube 32 is essentially a thermoresponsive switch with a sensing probe which spans the fuser cavity, and will hereafter be referred to as a switch. In a cold condition of the machine, the switch 32 is closed. In FIG. 3, reference character 32 refers to the switch in the diagram, and this same reference character is shown on the tube in the FIG. 2 in order to relate the two illustrations. I

The control of power centers about three relays and two control switches. Relay R-l operates two switches R-lA and R-lB. R-lA has only one normally closed switch contact. R-lB has two switch contacts S-1 and 8-2. Contact 8-1 is normally closed and contact 8-2 is normally open.

A second relay R-2 operates two switches R-2A and R-ZB. R-2A has one normally open set of contacts, whereas R-2B has a normally closed contact S-3 and a normally open contact 84.

A third relay R-3 operates only one switch R-3A with two contacts S-5 and 8-6. S-S is normally open'and 8-6 is normally closed.

When power is applied to 'the machine from the power lines L-l and L-2, through a switch not illus-' trated, relay R-l is immediately actuated through the closed switch 32. Power is also applied to R-2 momentarily, until R-lA opens. Closing of relay R-l immediately changes the condition of the contacts S-1 and 8-2, as well as opening the normally closed contacts of R-lA. R-2 is a delay-action relay, and therefore the momentary application of power does not produce action before the power is removed by opening of R-lA. Opening R-llA removes the power from R-2 before the delay action of R-2 enables the actuation of the contacts R-2A.

When the relay R-l changes the condition of the switches S-1 and S-2, power is supplied to a first potentiometer P-l through the normally closed switch 8-3 to the normally opened switch 8-2 which is now closed, and then to the normally closed contact 8-6 of the switch R-3A.

A circuit through potentiometer P-l is established to provide maximum power to the lamps 25 and 26. Rectifying diodes 52 and 53 are positioned to embrace circuitry in which a selected degree of resistance can be established by the potentiometer P-l, and two similar potentiometer P-2 and P-3. To use an established potential between'the diodes, the control circuit includes neon lamps 54 and 55 which will begin to conduct current at specifically defined voltages. Therefore, by the provision of condensers 56 and 57, the circuit is tuned to conduct to the base of twin silicone controlled rectifiers 58 and 59 in a precisely selectable period of time. Then, the amount of power supplied through the rectifiers 58 and 59 will determine the amount of voltage across the lamps 25 and 26 to establish the power output of the lamps. P-l provides maximum power output, and in the illustrated embodiment of the invention, is configured to supply 1,600 watts of thermo-energy.

After the chamber has reached its desired temperature level, the thermostatically operated switch 32 is said to be satisfied and will open. When switch 32 does open, the contacts S-1 and 8-2 will return to their original condition wherein S-1 is closed and 8-2 is open. Also, the contacts of R-lA will close.

Closing of the contacts of R-lA, however, causes the relay R-2 to be energized, closing its contacts R-2A after atime delay is satisfied. Once contacts R-ZA are closed, the relay R-2 is permanently energized. Relay R-2 does not drop out again until the main power lines to the machine are turned off.

Returning of the contacts 8-] and S-2 to their normal condition will break the circuit to potentiometer P-1 and will provide a closed circuit through potentiometer P-3 through the contact S-6. Potentiometer P-3 establishes a resistance between the diodes 52 and 53 which alters the current flow to the lamps 25 and 26 by changing the voltage upon the control circuit of the silicone controlled rectifiers 58 and 59. The resistance of P-3 is established to provide about 400 watts of energy to the lamps. This amount of energy is not sufficient to keep the chamber to the desired temperature. Therefore the switch 32 will, in a matter of a few seconds, close and re-energize the relay R-l, and thereby set up a third op erating condition.

With the relay R-2 energized as described, the contact 8-3 is open and the contact 8-4 is closed. Contact S-l is again opened and contact S-2 closed when switch 32 is closed. A circuit is then established through potentiometer P-2 through the contacts 8-4, 8-2 and 8-6. The voltage differential between the diodes is established by the potentiometer P-2 to cause a current supply to the lamps sufficient to product 1,000 watts of energy, in the particular illustrated embodiment of the invention.

One thousand watts of energy is more than sufficient to maintain the temperature of the chamber at the desired fusion intensity. Therefore, the temperature level within the chamber will begin to rise. As soon as the switch 32 is satisfied, it will open and reestablish the circuit through the potentiometer P-3. This cycling between potentiometers P-2 and P-3 will therefore continue and hold the chamber on a standby basis ready to accept a sheet delivered to the chamber at any time. The temperature may be slightly above a desired fuser level or slightly below, but in all events will be sufficiently close to serve the necessary purpose of providing sufficient heat to augment the radiation energy which is supplied to the face of the sheet whenever a sheet passes through the fuser. Such radiation takes place by the provision of a switch 60, which is shown in the FIG. 3 but not in the physical views of FIGS. 1

and 2. The switch 60 is a conventional switch, actuatable by contact of a sheet passing through the guide 17. Upon actuation of the switch 60 the relay R-3 is energized and the contacts of the relay R-3A are altered from their normal condition as shown in the drawing. 5-5 closes and 5-6 opens. Regardless of the condition of switch 32, a circuit is made only through potentiometer P-2 through contact S-4, which remains permanently closed after the original warm up period, and the now closed contact 5-5. If the switch 32 is-closed, the

contact S-lis open and therefore P-3 is inactive. If the switch 32 is open, there is no circuit through P-3 because the supply contact S-6 is open. The contact 5-3 is always open and therefore the potentiometer P-l is inactive. Accordingly, regardless of whether P-2 or P-3 is normally energized under the cycling operation described, whenever a sheet passes through a chamber and strikes the switch 60, the potentiometer P-2 is activated and causes a 1,000 watt energy supply to the lamps in order to radiate the sheet as it passes through thechamber. The sheet is therefore subjected to oven temperature of a level sufficiently high to warm the sheet and the toner thereon to urge the toner toward a fusing condition, and simultaneously the radiant energy will cause the toner to pick up an abundance of energy to supplement the oven temperature and assure a quick and complete fusion of the toner.

In the illustrated embodiment of the invention, the sheets are processed at a rate of 7 inches per second as contrasted with prior art practice of moving sheets at less than 3 inches per second through a high temperature oven. Furthermore, the distance from the entrance end 14 to the exitend 15 of the illustrated embodiment, is only 5.5 inches, thereby permitting a given increment of the sheet to remain in the oven only' 0.75 seconds. Such high speed processing is accomplished by having radiant power of high intensity throughout the entire length of the guide 17 and assures complete fusion but with minimum physical space required for the fusing chamber.

What is claimed is:

1. Fuser'apparatus for sheets electrostatically imaged with fusible toner, comprising:

a substantially closed chamber with an entrance opening and an exit opening;

a sheet guide means transparent to infrared extending from said entrance to exit;

electrical infrared means placed adjacent to one side of said guide means establishing a radiation field crossing said guide means substantially the entire distance from said entrance to exit;

an electrical control for said infrared means including thermosensing means sensing temperatures within said chamber; said control establishing an energy input to said infrared means in an alternating mode of energization between a higher level of energization above that necessary to establish in the chamber a selected temperaturerelated to the fusing temperature of said toner, and a lower level of energization below that necessary to establish said selected temperature;

sensing means for detecting the presence of a sheet within said chamber and for affecting said control means to establish the higher level energization condition so long as the sheet is in the chamber; and

conveyor means for moving a sheet through said chamber in a time interval less than would be required for fusing only by the ambient temperature therein. 2. Fuser apparatus for sheets electrostatically imaged with fusible toner, comprising:

a substantially closed chamber with an entrance opening and an exit opening; a sheet guide means transparent to infrared radiation extending from said entrance to exit; radiant energy output means for establishing an infrared field along 'said guide means; means for establishing a power input to said energy output means ofa magnitude greater than sufficient to cause the chamber interior to attain a predetermined maximum temperature; electrical control means including a sensing means sensing the temperature of said chamber for causing reduction of said power input whenever the chamber temperature attains said predetermined temperature; and means providing an override of the operation of said electrical control means to defeat the power reducing action thereof whenever a sheet is in the chamher. 3. Fuser apparatus for sheets electrostatically imaged with fusible toner, comprising:

a substantially closed chamber with an entrance opening and an exit opening; a sheet guide means transparent to infrared extending from said entrance to exit; electrical infrared means placed adjacent to one side of said guide means establishing a radiation field crossing said guide means substantially the entire distance from said entrance to exit; conveyor means for moving a sheet through said chamber in a time interval; an electrical control and power providing circuit for said infrared means including thermosensing means sensing temperatures within said chamber and providing a first high power input to said infrared means limited in time to a preoperation period sufficient to bring the chamber to a temperature above a designated mean average temperature and a low power input to said infrared means related to the heat loss characteristics of said chamber to supply energy at a rate less than the normal loss from said chamber, and a third power input of a capacity intermediate said first and second and supplying energy at a rate more than the normal loss from said chamber, said second and third output levels alternating to maintain said chamber temperature in a range to establish approximately said designated mean average temperature; and means for placing said infrared means in said third level responsive to a sheet passing through said chamber and operative without regard to ambient temperature in said chamber for only as long as the sheet is in the chamber. 4. Fuser apparatus for sheets electrostatically imaged with fusible toner, comprising:

a substantially closed chamber with an entrance opening and an exit opening; a sheet guide extending from said entrance to exit; said sheet guide formed in a grid configuration which will allow air circulation around a sheet passing through said chamber;

7 8 means for delivering thermal energy into said champassages connecting said plenum and collecting plenum; and asubstantially closed housing with an entrance opena blower connected to Supply air to Said plenum ing and an exit opening, said housing enclosing said chamber and defining therewith an air distribution plenum and a collection plenum;

said housing openings aligned with said openings of to an exhaust remote from Said P the plenum and spaced therefrom to provide air under pressure and an exhaust fan connected to draw air from said collection plenum and directed UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 7 ,497 Dated November 13, 1973 Inventor(s) I Donald R. Gray, et a1 It is certified that error appears in the above-identified patent and that said Letters. Patent are hereby corrected as shown below:

Page 1 [73] Assignee: Addressograph-Multigraph Corporation,

Cleveland, Ohio.

Signed and sealed this 2nd day of April 19714;.

(SEAL) Attest:

EDWARD M .FLETCHER ,J'R C. MARSHALL DANN Attesting Officer Commissioner of Patents =oR o-mso (10-69) USCOMM-DC man-Pee v d P.S. GOVERNMENT PRINTING OFFICE IO. 0-3-33l Q UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 3,772,497 Dated November 13, 1973 Inventor(s) Donald R. Gray, et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Page 1 [73] Assignee: Addressograph-Multigraph Corporation,

T Cleveland, Ohio.

Signed and sealed this 2nd day of April 19714.

(SEAL) Attest:

EDWARD M-FLETCHERQJR. C. MARSHALL DANN Attesting Officer Gormnissioner of Patents F M P 4 uscoMM-oc scan-ps9 3 I yrs. GOVERNMENT PRINTING OFFICE: 1969 o-ass-au A 

1. Fuser apparatus for sheets electrostatically imaged with fusible toner, comprising: a substantially closed chamber with an entrance opening and an exit opening; a sheet guide means transparent to infrared extending from said entrance to exit; electrical infrared means placed adjacent to one side of said guide means establishing a radiation field crossing said guide means substantially the entire distance from said entrance to exit; an electrical control for said infrared means including thermosensing means sensing temperatures within said chamber; said control establishing an energy input to said infrared means in an alternating mode of energization between a higher level of energization above that necessary to establish in the chamber a selected temperature related to the fusing temperature of said toner, and a lower level of energization below that necessary to establish said selected temperature; sensing means for detecting the presence of a sheet within said chamber and for affecting said control means to establish the higher level energization condition so long as the sheet is in the chamber; and conveyor means for moving a sheet through said chamber in a time interval less than would be required for fusing only by the ambient temperature therein.
 2. Fuser apparatus for sheets electrostatically imaged with fusible toner, comprising: a substantially closed chamber with an entrance opening and an exit opening; a sheet guide means transparent to infrared radiation extending from said entrance to exit; radiant energy output means for establishing an infrared field along said guide means; means for establishing a power input to said energy output means of a magnitude greater than sufficient to cause the chamber interior to attain a predetermined maximum temperature; electrical control means including a sensing means sensing the temperature of said chamber for causing reduction of said power input whenever the chamber temperature attains said predetermined temperature; and means providing an override of the operation of said electrical control means to defeat the power reducing action thereof whenever a sheet is in the chamber.
 3. Fuser apparatus for sheets electrostatically imaged with fusible toner, comprising: a substantially closed chamber with an entrance opening and an exit opening; a sheet guide means transparent to infrared extending from said entrance to exit; electrical infrared means placed adjacent to one side of said guide means establishing a radiation field crossing said guide means substantially the entire distance from said entrance to exit; conveyor means for moving a sheet through said chamber in a time interval; an electrical control and power providing circuit for said infrared means including thermosensing means sensing temperatures within said chamber and providing a first high power input to said infrared means limited in time to a preoperation period sufficient to bring the chamber to a temperature above a designated mean average temperature and a low power input to said infrared means related to the heat loss characteristics of said chamber to supply energy at a rate less than the normal loss from said chamber, and a third power input of a capacity intermediate said first and second and supplying energy at a rate more than the normal loss from said chamber, said second and third output levels alternating to maintain said chamber temperature in a range to establish appRoximately said designated mean average temperature; and means for placing said infrared means in said third level responsive to a sheet passing through said chamber and operative without regard to ambient temperature in said chamber for only as long as the sheet is in the chamber.
 4. Fuser apparatus for sheets electrostatically imaged with fusible toner, comprising: a substantially closed chamber with an entrance opening and an exit opening; a sheet guide extending from said entrance to exit; said sheet guide formed in a grid configuration which will allow air circulation around a sheet passing through said chamber; means for delivering thermal energy into said chamber; a substantially closed housing with an entrance opening and an exit opening, said housing enclosing said chamber and defining therewith an air distribution plenum and a collection plenum; said housing openings aligned with said openings of the plenum and spaced therefrom to provide air passages connecting said plenum and collecting plenum; and a blower connected to supply air to said plenum under pressure and an exhaust fan connected to draw air from said collection plenum and directed to an exhaust remote from said plenum. 